In the copending U.S. patent application of Cuneo et al., application Ser. No. 07/532,329, filed June 5, 1990, there is disclosed a method for constructing subassemblies for double-hulled vessel modules, laterally serially connecting the subassemblies to fabricate modules, longitudinally serially connecting the modules end to end to provide longitudinal midbodies for double-hulled vessels, and mounting bow and stern members to longitudinally opposite ends of the midbody to provide a double-hulled vessel, e.g., suitable for use as a very large crude carrier
In the subassembly construction according to Cuneo et al., both the inner skin and the outer skin of the hull structure are fabricated of generally cylindrically arcuately curved steel plates. The two skins are interconnected at corresponding longitudinal joints between the respective curved plates, by welds at opposite edges of stiffened flat plates which extend thicknesswise of the vessel hull structure, thereby dividing the hull structure into a plurality of longitudinally extend tubular cells, preferably extending on the bottom, sidewalls and deck of the longitudinal midbody of the vessel In a preferred construction disclosed in Cuneo et al., each subassembly includes a generally straight wall portion and half of a corner, so that a perimetrically extending series of eight subassemblies may be assembled edge to edge, reversing alternate subassemblies so as to abut half-corners to half-corners and straight ends to straight ends, with the resulting transverse cross-sectional profile of a module being rounded-corner rectangular. At the longitudinal centerline plane of the longitudinal midbody of the Cuneo et al structure, each module may be provided with a cell that serves as a corresponding segment of hollow keel, for accommodating duct work, piping and the like. Each module, according to the Cuneo et al. application, preferably includes at one end a transverse bulkhead which fully obstructs that end of the module, being perimetrically welded to the inner skin of the module on both the fore and aft sides of the transverse bulkhead. Other than the transverse bulkheads, the double-hulled vessel midbody according to the Cuneo et al. application has no significant transversally extending structural elements. Accordingly, double-hulled VLCC's may be constructed substantially completely out of welded-together and painted plates of mild steel, with little constructional/operational cost disadvantage in comparison with single-hulled VLCC's of comparable crude-carrying capacity.
The more recent U.S patent application of Richard A. Goldbach et al., application Ser. No. 07/678,802, filed Apr. 1, 1991, discloses improved method for fabricating the subassemblies which, as one result have a protective paint coating which is more durable, yet lighter in weight, with corresponding improvements to the subassemblies, modules, longitudinal midbody and vessel.
In the application of Goldbach et al , an improved curved-plate, double-hull tanker construction is provided, having reduced or eliminated transverse reinforcing structure in its midbody, except for bulkheads. The hull, though double, can compare in weight to conventional single hulls, despite being entirely made of mild steel plate. It is made of significantly fewer pieces, with a reduction in welding footage More of the steel is used in the form of plate, rather than more expensive shapes. Improved productivity is possible, resulting from standardization of parts, less scrap, greater use of jigs and fixtures, automated welding, blast-cleaning and painting, so that not so much staging is needed, the work environment can be safer, and the product can be produced at a lower unit labor cost. Preferably, cathodic epoxy painting is used for durability and reduction in problems due to blast cleaning, solvent evaporation and generation of refuse. Extending the double hull structure from the bottom and sides of the hull to the main deck can provide space for fuel oil to be located safely away from the skin of the ship, rather than in possibly vulnerable deep tanks at the stern. The constructional technique is believed to be applicable to vessel hulls in the 70,000 DWT to 300,000 DWT range. The vessel hull midbody module subassemblies may be assembled into modules, hull midbodies and vessels using the method and apparatus disclosed in Cuneo et al., U.S. patent application Ser. No. 07/532,329.
Conventional double-hulled tankers typically have had either no longitudinal vertical centerline bulkhead at all, or, if they have had one, it has been only one plate thick. Also, in conventional double-hulled tankers, fuel oil tanks for the propulsion and power engines of the tanker itself, and cargo slop tanks have been located forward or aft of the cargo tank-providing midbody section of the tanker.
In instances where a single wall longitudinal vertical centerline bulkhead is conventionally provided, its major intended functions are to improve tanker stability (by reducing the free-surface effect of liquids in cargo tanks), to provide a barrier separating different liquid cargos, and, in some designs, to contribute longitudinal strength to the vessel.
Typically, additional bulkhead reinforcing structure must be provided if a conventional single wall longitudinal vertical centerline bulkhead is provided, and the presence of the additional reinforcing structure inside the cargo tanks makes cleaning the cargo tanks more difficult inasmuch as there is more surface area and more complex surface topography that needs to be cleaned.